What is base-can positioning?
Setting the base can in its hole on the exact survey point, at the design height, level and aligned with the runway axis (or the direction the design shows for that light) — and holding it there — because once the grout has set, the position is very hard to change.
Base-can positioning is placing the can in the excavated hole so that it is on its surveyed position, at the design height, level, and aligned with the runway axis. The fixture later bolts to this can, so the can decides where the light is and which way it faces.
Check it before any grout is placed. Once the grout has set, a can that is off position, tilted or twisted is hard to correct and normally has to be cut out and set again. Use an alignment jig referenced to a surveyed line, hold the can firmly so it cannot move or float, and plug the openings so grout stays out. Work to the airport’s permit-to-work and keep the area clear of debris.
- Mark the point. Transfer the centre and the runway axis from the survey to the hole.
- Lower the can. Place it in the hole on its support, with cable entries turned toward the duct.
- Set the height. Bring the flange to the design level, so the fixture will finish at the pavement surface within the specified tolerance.
- Level it. Check the flange level in both directions.
- Align it. Fit the alignment jig and set the can aligned with the runway axis (or the direction the design shows), at the design offset.
- Hold and recheck. Secure the can, plug its openings, and recheck all four before grouting.
Frequently Asked Questions
Q1What is base-can positioning in airfield ground lighting?
Base-can positioning is placing the base can in its excavated hole so it sits on the survey position, at the design height, level, and aligned with the runway axis (or the direction the design shows for that light), then holding it there until it is grouted. The fixture later bolts to this can, so the can fixes where the light is and which way it faces.
Q2Why does the height of the base can matter?
The top of the can sets where the fixture finishes relative to the pavement surface. Too high and the fixture can stand proud of the surface; too low and it can sit in a depression that collects water and debris. The exact finish level comes from the design and the manufacturer’s data.
Q3Why must the can flange be level?
The fixture seats on the flange, so a tilted flange tilts the fixture, which can leave it rocking on the can or pointing its light off its intended direction. Check level in both directions with a spirit level or levelling tool, not just one.
Q4How is the can aligned to the runway axis?
Normally with an alignment jig or template that locates the can’s bolt pattern or orientation marks and is referenced to a surveyed line or string line along the runway axis. The jig also holds the can in place while it is secured.
Q5Why face the cable entry toward the duct?
So the cable can run from the duct into the can in a smooth sweep instead of being forced round a tight bend. Which cables enter depends on the arrangement: usually the secondary cable, or both primary and secondary where the isolating transformer sits in the can. Check the cable entries against the duct they will use before the can is fixed, since the can cannot be turned afterwards.
Q6What happens if a can is set in the wrong position?
Once grout has set, a misplaced can is difficult to correct and normally means cutting it out and re-setting it. The light would otherwise sit off its design position or face the wrong way, so check position, height, level and alignment before any grout goes in.
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